-- -- -- the very latest on the investigation unfolding authorities working this morning to connect so many dots. One big clue could be Monday's date April 15 the anniversaries from some of the most harrowing incidents in domestic terror are coming this week. And ABC's Pierre Thomas in Washington has been tracking. All the latest and has that right now -- good morning here. Good morning -- my sources tell me it's the evidence on scene and witnesses that will break open this case. The list of potential suspects could be long because investigators know. This stretch of April is one with a dark history. This Friday April 19 is also the anniversary. Of two of the most dramatic days in the country's recent history. In 1993. -- 51 day standoff between federal law enforcement and branch Davidian leader David Koresh ended with eighty dead. Including 25 children when -- refused to surrender peacefully. On the same day two years later Timothy McVeigh bombed the Alfred Murrah Federal Building in Oklahoma City killing 168. Including nineteen children in the building's day -- center. That attack was specifically not designed as patent act for the government's role in Waco two years earlier. For those who hate America and know something of its history Monday had particular -- in Massachusetts. Monday was a state holiday. Patriots day commemorating the first shots fired in the American revolution. During the battles of Lexington and Concord farm near Boston in 77 -- -- But the real patriots day is April 19 that is the date that counts for people on the extreme right in the United States. As it happens Massachusetts celebrates Patriot's Day. On the third Monday of every -- the month. But for every conspiracy theory about domestic extremists or international terrorist leaders who spent -- has seen this year random senseless violence. -- at the innocent and vulnerable in public places soft targets. On this day six years ago the Virginia Tech massacre and this Saturday April 20 marks fourteen years since the deadly Columbine school shooting. Investigators are mindful of all of this but my sources tell me today the priority is simply to go where the evidence point.

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